//xhr-全局

let xhr;

if(window.XMLHttpRequest){
    xhr=new XMLHttpRequest();
}else{
    xhr=new ActiveXObject("Microsoft.XMLHTTP");
}

// myAjax(method,url,params,callback,async)

function myAjax(method,url,params,callback,async) {
    if(async==undefined){
        async=true;//异步
    }

    xhr.onreadystatechange=function () {
        if(xhr.readyState==4&&xhr.status==200){
            callback()
        }
    }

    if(method=="get"){
        xhr.open(method,url+"?"+params,async);
        xhr.send(null);
    }else if(method=="post"){
        xhr.open(method,url,async);
        xhr.setRequestHeader("Content-type","application/x-www-form-urlencoded");
        xhr.send(params)
    }
}